In the electrical trade, electric wires are run through metal tubular conduits where the conduits are joined with electrical meter boxes, circuit breaker boxes, electrical gutters and other electrical apparatus equipment where it is necessary to join the pieces of the outer protective metal covering. To this end, electrical manufacturers have prepared knockouts in the sides of the electrical meters, boxes, gutters and the like to accept the electrical metal tubular conduit which contains the electrical wires. Normally, a typical concentric knockout will consist of a partially punched interior circle and then a series of three or four partially pre-punched concentric rings. When it is desired to enlarge the hole beyond the center prepunched portion, these concentric rings must be consecutively removed until the desired hole diameter is achieved.
The concentric rings have been pre-punched through the majority of the circumference, however, there is generally two to four lands in the ring where they have not been punched. These lands, which normally are 1/8 to 1/4 of an inch across, must be cut in order to remove the concentric ring and thereby enlarge the hole.
Heretofore, there have not been problems in removing the central plug, however, there has been great difficulty in cutting the lands of the concentric ring. Different means have been adopted to cut these lands, including hammering on the concentric ring until the land has broken or just by drilling out the concentric ring itself. In the case of hammering upon the ring, a substantial danger is run in deforming adjacent knockouts or surrounding metal. Other methods are to apply a cold chisel to the land and thereby sever its connection between the concentric rings.
Perhaps the most popular way of cutting the land is to grab the inner concentric ring with the pair of electricians pliers and then to twist the ring until the land is twisted in half and the ring freed. The methods above described have not been satisfactory in practice and it is most common now for electricians to hammer out all knockouts and then apply reducing washers with bushings to achieve the desired opening or to cut separate holes that they need in the electrical equipment by some other method such as a hole punch. This latter method, however, does not take advantage of the pre-punched knockouts which have been provided by the manufacturer nor is this method fast or efficient.
Accordingly, there is a great need for a shearing tool which permits rapid shearing of the concentric ring lands in order that they may be removed for installation of electrical tubular conduit.